Absorption of the C H Stretching Fundamentals in Pure Ethylene to High Pressures and Temperatures

The infrared absorption of the v 9 and v 11 stretching fundamentals in pure ethylene was measured at supercritical temperatures between 26°C and 200°C to a maximum pressure of 2000 bar. The density and temperature dependence of the absorption intensity and of the wave‐numbers of maximum absorption are reported. The decrease of the v 9 molar integrated absorptivity toward the highest densities is interpreted as being due to the importance of repulsive interactions in dense pure ethylene. The position of the v 11 band maximum provides a measure for the extent of rotational freedom in the fluid state.